Electroless nickel plating



United States Patent 3,424,597 ELECTROLESS NICKEL PLATING Charles R.Shipley, Jr., Newton, Mass, assignor to Shipley Company, Inc., Newton,Mass., a corporation of Massachusetts No Drawing. Filed Apr. 8, 1966,Ser. No. 541,059 U.S. Cl. 1061 7 Claims Int. Cl. C23c 17/02 ABSTRACT OFTHE DISCLOSURE An electroless nickel plating composition of the nickelcation-hypophosphite anion type characterized by the addition of aneffective amount of a solution soluble polymer. Nickel deposited fromsolution is readily plated without treatment to remove oxide coatings.It is believed that the addition to the plating solution provides athin, protective layer over the nickel plated surface which is readilyredissolved in a subsequent plating bath, thereby preventing oxidationof the nickel in water or in the atmosphere.

This invention relates to improved processes of electroless nickelplating of catalytic surfaces employing baths of the nickelcation-hypophosphite anion type, the nickel ions being reduced to metalby the hypophosphite ions. Electroless plating refers to plating bychemical reduction in the absence of an external electric source.

Electroless nickel deposition of the above type is well known and isdisclosed for example in United States Patents Nos. 2,532,283,2,762,723, 2,935,425, and 2,999,- 770, which disclose suitablematerials, concentrations, operating temperatures, pH conditions andvarious additives such as buffers, complexing agents for the nickelions, and stabilizers. Deposition occurs in the presence of a catalyticsurface, generally a variety of metals as disclosed in the abovepatents. Also, non-catalytic surfaces, such as plastics, ceramics, orother dielectrics, may be sensitized with catalysts as disclosed in theabove patents and as also disclosed in United States Patent No.3,011,920.

Heretofore in the plating of nickel, whether electrolytically or byelectroless deposition but especially the latter, the nickel surfacerapidly becomes passive upon removal from the plating composition. Thesurface undergoes oxidation in water or in the atmosphere to form atenaciously adherent oxidized surface resistant to further reaction.This surface resists overplating, which requires a substantially purenickel surface, either with additional nickel or with dissimilar metalssuch as a protective coating of gold. Electroless nickel platings areparticularly resistant to overplating, after storage, thought to be dueto inclusions of impurities such as nickel phosphide. Electroless nickelplating obtained by the use of compositions such as described abovebecome passive if stored for as little as 60 minutes. Storage overnightresults in surfaces difiicult or impossible to activate, a conditionwhich grows progressively worse with time.

It is accordingly the principal object of the present invention toprovide electroless nickel compositions of the nickelcation-hypophosphite anion type which maintain an activated surface forperiods of storage at least two weeks or longer such that they may bereadily overplated with nickel or dissimilar metal.

In accordance with the present invention the improved electroless nickelcompositions comprise aqueous solutions of a source of nickel ions in anamount sufiicient to provide a useful deposit and a source ofhypophosphite ion in an amount sufficient to serve as a reducing agenttherefor, characterized by the inclusion therein of an effective amountof a solution-soluble polymer which appears to provide on the surface athin protective layer readily resoluble in the subsequent plating bath.The amount of the ICE addition is not critical, small amounts providingsome improvement while large amounts short of undue increase in solutionviscosity are tolerable. Amounts greater than incidental impurities upto about 5.0 grams per liter are preferred, and from about 0.1 to about1.0 gram per liter are most preferred.

Suitable polymers include Gantrez M, a polyvinyl methyl ether;copolymers thereof such as Gantrez AN, believed to be a copolymercomprising alternating units of methyl vinyl ether and maleic anhydride;and Thickener L, a modified copolymer of Gantrez AN; all of the GeneralAniline & Film Corp; DX-840 Resin, believed to be a polyethylene maleicanhydride random copolymer of the Monsanto Chemical Company; SMA, astyrene maleic anhydride random copolymer of Sinclair Petrochemicals,Inc.; cellulose ethers such as CMC, carboxymethylcellulose; HEC,hydroxymethylcellulose; and CMHEC, carboxymethylhydroxyethylcellulose;available from Hercules Powder Company; and modified polyacrylamidesavailable in various grades under the trademark Reten from the HerculesPowder Company. While the reason for the effectiveness of thesematerials is not completely understood, it is, as indicated above,believed to be related to the provision of a protective coating readilyre-soluble in the subsequent plating composition. Molecular weight doesnot appear to be critical although intermediate grades are currentlypreferred.

The above polymeric additives are useful in substantially all of thenickel cation-hypophosphite anion types heretofore known. Illustrativeexamples are given below.

EXAMPLE I Ingredient:

NiSO 6H O g./l 20 NaH2PO H O g./l 30 Hydroxy-acetic acid g./l 28 GantrezAN-139 g./l 0.2

NH OH, to pH 4.5-5.0. Water, to make 1 liter. PbC1- as stabilizer ppm.Pb 1 Platings made at 200 F. with the above composition over steelmaintain an activated surface capable of reimmersion in the solution andadditional adherent plating of nickel for a period of at least twoweeks. Furthermore, the platings may be subsequently immersed, afterstorage for at least two weeks, in dissimilar plating compositions suchas the replacement gold compositions disclosed in copending applicationSer. No. 244,949, now US. Patent No. 3,266,929, and dissimilar metalplated thereover.

As additional examples, each of the following polymeric products ormixtures thereof can be substituted for the above polymer GantrezAN-139, in a similar amount and with substantially the same result.

In the above examples nickel sulfate is the source of nickel cations,sodium hypophosphite the reducing agent, and hydroxyacetic acid a knowncomplexing agent for the nickel ions. Lead chloride as stabilizer wasused in accordance with US. Patent No. 2,762,723. Other suitable agentsmay be substituted and buffers employed where desired. The addition ofpolymer does not substantially change useful concentrations, pH rangesor operating conditions as heretofore known and as illustrated in theabove patents. pH may range from about 3 to 11 but is preferably on themildly acid side of neutrality.

It should be understood that the foregoing description is for thepurpose of illustration and that the invention includes. allmodifications falling within the scope of the appended claims.

I claim:

1. In an electroless nickel plating composition comprising an aqueoussolution of a source of nickel cations in an amout sufiicient to providea useful deposit and a source of hypophosphite anions in an amountsufiicient to act as reducing agent therefor, the improvement comprisingthe addition of a polymer selected from the group consisting ofpolvyinyl methyl ether, a copolymer of methyl vinyl ether and maleicanhydride, a copolymer of polyethylene and maleic anhydride, a copolymerof polystyrene and maleic anhydride, carboxymethylcellulose,hydroxymethylcellulose, carboxymethylhydroxyethylcellulose,polyacrylamide, and mixtures thereof, said polymer being present in anamount effective to permit overplating with nickel after storage.

2. A composition according to claim 1 wherein said polymer is acopolymer of methylvinyl ether and maleic anhydride.

3. A composition according to claim 1, wherein said polymer is presentin an effective amount greater than incidental impurities up to about5.0 grams per liter.

4. A composition according to claim 1, wherein said composition has a pHbetween about 3 and 11.

5. The method of electroless plating which comprises contacting acatalytic surface with a composition according to claim 1 to depositelectroless nickel, and removing said surface from contact with saidsolution.

6. Method of plating according to claim 5, further characterized by theadditional step of overplating said nickel after storage with nickel orgold.

7. A composition according to claim 2, wherein said polymer is presentin an effective amount greater than incidental impurities up to about 5.0 grams per liter.

References Cited UNITED STATES PATENTS JULIUS FROME, Primaly Examiner.

L. HAYES, Assistant Examiner.

US. Cl. X.R. 117-130,

